Experimental and Theoretical Study of the Terahertz Absorption Spectra of Crystalline Saccharides

Terahertz time-domain spectroscopy has been used to measure the full dielectric function of polycrystaltine D-glucose and D-mannose. A number of well-resolved absorption peaks were observed in the frequency range 0.2-3.0 THz, which are interpreted as originating from inter-and intra-molecular vibrational modes. In parallel with the experimental study, density functional theory was applied to obtain structure and vibrational frequencies of the saccharides. The calculated results are in reasonable agreement with the experimental data. The comparison between experimental and theoretical study shows that far-infrared absorption features are highly sensitive to the structure and spatial arrangement of molecules.